1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method for forming an image by ejecting ink toward a recording medium in the form of droplets, and more particularly, to an image forming apparatus and an image forming method for forming an image on a large area recording medium, such as a flexible sheet made of polyvinyl chloride (PVC), using an ink containing a solvent and a pigment as a coloring material.
2. Description of the Related Art
Inkjet recording apparatuses provided with an inkjet head in which a plurality of nozzles are arranged, have been known in the related art as image forming apparatuses. An inkjet recording apparatus of this kind forms dots on a recording medium so as to form an image, by ejecting ink in the form of droplets from nozzles toward the recording medium, while causing the inkjet head and the recording medium to move relatively to each other.
In the inkjet recording apparatus, one image is formed by combining dots that are formed of ink droplets ejected from the nozzles and deposited on the recording medium. In recent years, with the spread of digital cameras, and the like, the printing of digital images by means of an inkjet recording apparatus has become a common practice, and the demand in the image formation of high-definition and high-quality, such as photographic prints, has been increased.
In order for the inkjet recording apparatus to form images of high quality, removal of the ink solvent is an important issue, and it is desirable that the ink solvent be removed swiftly, immediately after the ink droplets are deposited on the recording medium.
One ink solvent removal method has been known in the related art in which the solvent is evaporated (dried) by heating the recording medium uniformly after depositing the ink droplets. Moreover, there have also been methods in which the heating energy efficiency is improved by selectively heating only those portions (the printed areas) where ink has been deposited on the recording medium.
For example, Japanese Patent Application Publication No. 9-314818 discloses a method in which the ink deposition areas on print paper are identified on the basis of print information, and those ink deposition areas on the print paper are selectively heated while the heating device constituted of a plurality of heating bodies that are arranged in a lattice configuration is caused to move according to the conveyance speed of the print paper.
However, in the method described in Japanese Patent Application Publication No. 9-314818, it is very difficult in practice to raise the temperature rapidly by heating only the printed areas on a moving print paper, because of delay in the response of the heating bodies. Moreover, since the thermal capacity of the print paper is generally small, then it may be difficult to achieve sufficient drying of the ink by heating the print paper before printing alone. Even if heating is carried out both before printing and during printing, there is still concern in that depending on the material of the print paper, the print paper is deformed due to thermal expansion caused by the partial heating of the print paper, resulting in degradation of the image.